[AJCoholic]

Tonight I went out after work to test fly the newly reapired Super Reaper, with the new Moore's 66 engine in it. I was a bit nervous of the trouble I had last year with the landings, but I was also eager to see how going up to 20 pounds of thrust was going to make the plane handle.

Upon start up, taxiing out to the runway I noticed that each little bump I hit the engine would cough a bit, and then after a big bump it quit. I am 100% positive the BMV ultimate air trap header was the cause, it must still have had some air trapped in the membrane and when it hit a bump, it released enough to kill the engine.

I went back to the pits, started up the engine and ran it up and down (perfect) and tried to shake the plane while it was running to get rid of the air.

Then I restarted it, and went to take off. The extra power sure makes acceleration FAST! I took off, and started my climb out and..... SILENCE!! Doh, what a time to have a dead stick. I mamaged to get the nose down, and headed back for the runway but landed in the farmers field. Went to get the plane, no damage!

So, back to the pits. I started it up, did the shake-shake thing. It ran up and down no problem and I thought I got it out. Refueled and restarted, back out to the runway. This time my taxi didnt give any hiccups so I thought it was OK. Hold the brakes, throttle up and WHOOOOO!!! It sure gets up to speed FAST and no bouncing on the nose wheel, now that I moved my main gear back. I eased back the elevator and it took off, and I held it about 5 feet off the deck and then slowly climbed out. What a nice smooth flying plane, I allmost forgot. Then, as I started my climb out and turn, deadstick again. Doh! This time I was too far out to make a good landing, and I hit a bit hard. The main gear playwood plate came off the bottom of the fuse, but nothing else damaged. Whew! Its an easy reapair.

I guess I will have to recirulate the fuel and shake the UAT tank before I attempt another flight. I need to get ALL the air out of the membrane. I went through this with the other UAT I have, and since I did most of my running on the bench, by the time I got it into the plane it was fine. This one is brand new,and I only ran the Moore's engine a few tanks to get familiar with it (it runs great by the way).

Will try and fix it tomorrow and get back out this weekend!

I cant wait to get to ring it out - from what I saw this evening, the extra oomph of the larger engine will make this one awesome flying machine!

[Helijet]

Hi Andrew

I have used the UATs now for several years and have found them to be quite effective. I normally fill my tanks several days before the big test flight then defuel all the tanks except the UAT. That ALWAYS remains full. I normally do a good shake of the plane like you suggest but only on the first run. I also found that it is best to position the UAT on edge at 45 degrees or higher ( the two brass fillers in the top most position ). This allows the airbubbles to escape the UAT easily. Also check all your festo connections. At full power I have seen a small improperly seated festo connector allow a lot of air.

Just some thoughts
Dean l

[Guest]

Excellent news re. Reaper coming alive again....Glad you made it back OK, however I am not so sure your UAT is at fault.

The slanted attitude is necessary to keep the air at the top corner of the tank.

Check all your electrical connections, and I am saying this based on your comment:
"I noticed that each little bump I hit the engine would cough a bit, and then after a big bump it quit"

Of course air bubbles in the fuel line feeding the turbine should show if the UAT is at fault.

Lookign forward to seeing you at the Quinte meet.

[AJCoholic]

Dean,
The engine runs great (the whole tank at all throttle settings) if it is stationary - so I presumed the air is still clinging to the membrane and needs to be "shook off". I remember when I first built the reaper and had the wren in it, I had it quit a number of times due to the same problem, but it was on the ground not in the air.

I will do another stationary run or two with the UAT out of the fuse and shake it thoroughly as BVM ststes in the manual.

At least now I know how the Reaper glides!

But I got a taste of power, and I like it!!

[AJCoholic]

Peter,
I will check everything out tomorrow evening. All connections, all fuel fittings, etc.

Obviously since it runs great on the ground, when held stationary it has to be something (air or other) that is happening on shaking the fuse.

Why I thought it was the air, is that the initial taxiing was very pronounced, allmost every bump it hit the engine definitely changed a split second in pitch, and after I shook the plane, it was allmost gone and on my last taxi to the runway and the entore take off run the engine didnt "miss". WHy it decided to quit in the air who knows... ?

I am pretty glad that I fixed up the plane and it seemed to fly great for the brief time I was up. It flew straight and level without trimming it. I was most impressed with the take off run though, and the speed it got up to in the 300 foot run.

[Len]

Hi Andrew,
I am so pleased to hear you are happy with the engine! The method I use to "break in" the UAT's is to run the pump disconnected from the TCU on a 2 or 3 cell pack ( I prefer 2 cells ) with enough fuel in the tank to allow no bubbles through the UAT, and run the fuel pump's output tube into the main tank's vent line (closed loop). After about 15 mins, I have found the UAT is all set. Of course you should shake the UAT a few times during this process.

As Dean says, never drain the UAT unless absolutely necessary and there will never be a problem with it. The ones in my Delta and HotSpot are a few years old and work perfectly. This "break in" method comes from BV himself by the way.

Enjoy,
Len

[AJCoholic]

Len,
I was thinking that same thing after last night - I am going to disconnect the UAT and run my pump in a closed loop to recirculate the fuel untill it is purged.

The engine starts up excellent, runs great at all rpms and seems to transition up and down just fine. After I figured out the GB controller and got the high end set it doesnt overshoot and the starts are flawless. The temps are right on now too, after I got the probe positioned correctly And the idle seems to be rock steady.

I do have a UAT running with my Wren set up since 2002 - and I have never de-fueled it ever. I know you arent supposed to and I make sure it stays full of fuel.

[AJCoholic]

OK, problem solved I am pretty certain.

This evening I ran the engine again, and tried to duplicate the shut down. (oh yes, I repaired the damage from last night during lunch, nothing bad just epoxied the LG plate back onto the fuse)

Well, I got it to shut down, and it WAS due to air bubbles, you could CLKEARLY see them appear in the line and travel through the line to the engine which would then hiccup. But, they werent from the UAT.... they were from the FUEL FILTER!! Doh!

When I tapped the filter, a large group of bubbles came out and I knew it was that. I shook the jet while it was running and it quit. So, I purged the air out of the filter (I am using a lawn mower filter I modified for the jet and it is fairly large diameter, and I forgot to purge the air from it) and I ran the engine again, tapped the filter violently and no more air! Also, the engine couldnt be made to quit.

So, I am 100% certain it was the cause and now I am ready to re test fly... again!

Love it when a problem gets solved! Thanks for the tips and advice guys. Thats what I appreciate!

[Shaunrbell]

I had the exact same thing happen in a 35% Extra. Bubbles would appear from the large fuel filter I was using. I though purging would fix the problem, but the bubbles would just reappear! It was almost like the fuel was cavitating from the large filter. I know it sound nuts, but as soon as I went to a smaller filter the bubbles stopped. Strange but true.

Shaun Bell

[AJCoholic]

Shaun,
In the jet, once the air is purged it never gets emptied from the line (in my case, the filter is located right before the fuel pump, and the fuel shut off valve is on the other side. Since I never drain the tanks fully, and the line from the header tank through the shut off/filter/pump to the engine allways remains full of fuel, the filter doesnt collect fuel.

I have the same filter in my other jet, and that fuel system hasnt been emptied since spring 2002, and its been in three different planes! (I just took the entire plumbing system from plane to plane) and I havent ever had a problem other than when It was newly installed.

In the jet, the UAT (header tank) contains a special membrane that the fuel must pass through, which will not allow air to pass through. Unlike in a traditional gasoline engine plane where if the clunk gets some air for a second during a manouver, it goes into the line immediately and travels through to the engine.